In most apparatus for applying or sealing fixing elements or plugs, particularly in steel or concrete substrate materials, loading of the plugs is carried out from the front or the muzzle of the apparatus and it is not always satisfactory. Just before firing, the plugs are in fact already in contact with the substrate material, and not with the plunger or piston of the firing or driving apparatus, so that at the moment of firing, no initial speed is imparted to the plugs.
Apparatus have already been proposed which reduce this drawback, with loading of the plugs from the rear to the front, through means of an opening formed in the barrel. But this solution does not offer sufficient guidance and safety.
The best solutions proposed up to now are those of apparatus provided with a tilting plug guide, like those of FR-A-1531056, U.S. Pat. No. 4,349,141, FR-A-2409826.
The apparatus of FR-A-2409826, which is in fact an indirectly fired apparatus with a plunger and a plunger return catch, comprises a plug guide mounted on a cap screwed into the barrel and pivoting automatically under the action of a sleeve, for operating, opening, and closing the barrel, slidably mounted on the cap.
The apparatus of U.S. Pat. No. 4,349,141, which is in fact also an indirectly fired apparatus with a plunger, but not with a plunger return catch, comprises a plug guide mounted for pivoting automatically in a sleeve, for operating, opening, and closing the barrel, slidably mounted on the barrel. It is the plug guide which, during closure, returns the plunger to the firing position.
The apparatus of FR-A-1531056 is also an indirectly fired apparatus with a plunger, with a plug guide mounted for pivoting on a sleeve mounted slidingly on the barrel, and without a return catch, the plunger being returned to the firing position during closure by means of the fixing elements themselves.
These last types of apparatus are well suited to fixing so-called "rivet head" plugs, which can be driven at a non-zero initial speed by means of a plunger of large rod cross-section, the same as that of the plug heads, which is favourable to proper fixing. But they are much less well adapted to plugs provided with a screw thread, or with a threaded head, and particularly with a threaded head of small cross-section. In this case, the plugs must be raised by a guide cap which does not always fully fulfil its role and which is often difficult to withdraw after fixing. Alternatively, the throughput cross-section of the plug guide as well as the cross-section of the plunger rod can be reduced correspondingly, but with the risk of the plunger rod then twisting at the moment of firing.
FR-A-2336216 is arranged so as to provide a solution to the problem of propulsion of threaded plugs, in so far as it comprises a plunger rod of which the front end is hollowed out to receive the threaded heads of the plugs and thus ensure, at the time of firing, guidance and initial speed.
But the supply of a fixing element in the apparatus of FR-A-2336216 is carried out by means of its muzzle with the aid of a tiltably mounted thruster, which requires a manual operation on the part of the operator.